The present invention relates to a method for simultaneously applying a plurality of liquids containing organic solvents to a continuously moving nonmagnetic carrier so as to form mutually stacked layers thereon.
The recent trend has been to increase the density of recording on a magnetic recording medium while decreasing the thickness of the medium. To be able to accomplish this, conventional methods of applying a liquid to a nonmagnetic carrier to form a single magnetic layer thereon have been replaced by method of applying plural liquids to a nonmagnetic carrier to form a plurality of magnetic layers thereon. The reason is because a magnetic recording medium having plural magnetic layers has much better magnetic recording properties such as magnetic data storage capacity than a magnetic recording medium having only a single magnetic layer.
The required number of the plural magnetic layers is two to several. In a conventional method of applying liquids to a nonmagnetic carrier to form such a plurality of magnetic layers, the liquids are applied to the carrier and then dried one after another, as disclosed in the Japanese Patent Applications Nos. 43362/79 and 43816/83 and the Japanese Unexamined Published Patent Applications Nos. 119204/76, 51908/77 and 16604/73.
Since application and drying are repeated in the above-mentioned conventional method, the productivity of the method is generally low and the amount of equipment required is large, and the equipment is bulky and expensive. Moreover, a magnetic recording element is likely to be unmatched on the boundary between the magnetic layers to cause modulation noise or the like.
Therefore, a method of applying plural liquids to a nonmagnetic carrier and then drying the liquids simultaneously to form a plurality of magnetic layers on the carrier has been desired.
A method of simultaneously applying plural liquids to a nonmagnetic carrier to form a plurality of magnetic layers thereon is disclosed in Japanese Unexamined Published Patent Applications Nos. 212933/87 and 124631/87. With this method, however, chromatic nonuniformities and longitudinal streaking are more likely to occur in the magnetic layer, even at a low speed of application, than in the above-mentioned method of repeatedly applying and drying the liquids, if the liquids are a nonmagnetic liquid containing an organic solvent and a magnetic liquid containing an organic solvent or are magnetic liquids containing organic solvents. The occurrence of chromatic nonuniformities and longitudinal streaking cause a conspicuous deterioration of the electromagnetic converting property and external appearance of a magnetic recording tape.
Further, for some combination of liquid compositions, the upper liquid cannot be uniformly applied over the lower liquid on the carrier, namely, two distinct layers cannot be properly formed from the liquids, or the upper liquid cannot be applied on the lower liquid on the carrier at all. This problem becomes more prominent as the applied quantities of the liquids are decreased (that is, the thickness of the layers of the liquids on the carrier are decreased) or the speed of application is increased. Even if the liquids can be applied at some thicknesses to the carrier, the surface of the magnetic recording tape may not be good. If the tape is a video tape or the like and has such a problem, a high video noise level is generated with the tape.
In a method of applying liquids to a carrier to form a plurality of layers thereon to manufacture a photographic photosensitive material, chromatic nonuniformity and longitudinal streaking occur in the layer. One of the causes of this has been presumed to be the fact that the boundary between the layers of the liquids is disturbed due to the differences between the viscosities of the liquids. Thus, the problem has been prevented by reducing the difference between the viscosities of the liquids for the mutually adjacent layers. Since the liquids for the photographic photosensitive material are Newtonian fluids whose physical properties greatly depend on the static viscosities thereof, which can be easily predetermined by appropriately selecting the compositions of the liquids, the problem can be prevented by preparing the liquids so as to make the static viscosities thereof closer to each other.
On the other hand, the magnetic liquids used for the magnetic recording medium are generally non-Newtonian fluids whose viscosity is not constant but varies in accordance with various conditions. For that reason, it has been found difficult to control the magnetic liquid, and hence the above approach of suitably establishing the relative viscosities of the liquids can be only implemented by empirically determinations. Under such circumstances, it is very difficult to obtain a magnetic recording medium of uniform quality with good productivity.